The present invention relates to a device for transmitting movement to fans for cooling the cooling liquid of motor vehicles, comprising a coupling of the electromagnetic type with front magnetic linkage and adjustable induction current.
It is known that, in the technical sector relating to cooling and the cooling liquids contained in motor-vehicle radiators, there exists the need to force air onto the radiator itself in order to obtain more rapid dissipation of heat from the liquid to the exterior, said forced-air flow being obtained by causing rotation of a fan which is normally mounted either on the shaft of the water pump or on a driven shaft carrying a pulley which receives movement from a belt actuated by the crankshaft.
It is also known that said fan must be made to rotate only when a certain predefined temperature of the water is reached, said temperature being detected by means of a thermostat which actuates an electromagnetic clutch, closing of which starts rotation of the fan.
Such electromagnetic clutches have the drawback, however, that they start rotation of the fan at the speed of rotation of the actuating pulley, without the possibility of varying the speed of rotation of the fan depending on a desired variation in operating speed of the latter.
More particularly, a motor-vehicle fan should be able to rotate:
at a lower speed than the speed of the drive shaft for cooling in conditions where there is a low external temperature;
at a speed equal to or even greater than that of the drive shaft in the case of higher external temperatures or use in demanding conditions which cause overheating of the engine;
at zero speed or with a fan which does not rotate at all or which remains in an idle condition with respect to the drive shaft, in the case of particularly low temperatures at which further cooling is of no use or even damaging.
In an attempt to obtain these performance characteristics, couplings of the mixed type with electromagnetically operated friction clutches and drive couplings based on the use of parasitic currents generated by the rotation of a conducting element in the vicinity of permanent magnets have been developed.
This solution is, for example, known from DE 32 03 143 which describes an arrangement in which the crankshaft is connected to the rotor of an electromagnetic clutch to which an armature connected to the fan for direct drive is coupled, whereas, for slow speeds, the engagement between a conducting disc, rotating together with the drive shaft, and the permanent magnets integral with the fan is used, said engagement causing transmission of movement at a slow speed on account of the relative slippage between the two parts.
With this solution, however, it is not possible to obtain either the idle (stopped) condition of the fan or a speed which is greater than that of the drive shaft.
In order to overcome these drawbacks, EP-0 317 703 describes a coupling which, re-applying the solution of the prior publication DE-32 03 143, also envisages a second electromagnetic clutch which, in combination with the other ones, is able to achieve three different operating conditions, but not a speed of the fan greater than that of drive shaft.
Both the solutions also have a structural limitation due to the fact that the slow speed is predefined by the size of the electromagnet forming the operating system for the clutch and it is therefore not possible to regulate the slow speed of rotation of the fan in a variable range corresponding to the actual temperature conditions of the engine.
It is an object of the invention to provide a device for transmitting the rotational movement to a fan cooling the cooling liquid of motor vehicles, which is operated by a single operating means and which allows the fan to run with a number of revolutions which can be controlled and adjusted according to the actual cooling requirement of the engine, which also includes the possibility of keeping the fan stopped in the case of very low external temperatures.
A further object is to provide such a device which can be controlled by means of direct detection of the temperature of the cooling liquid and allow selection of both manual and automatic operation.
These technical problems are solved according to the present invention by a device for transmitting the movement to a fan cooling the cooling liquid of a motor vehicle, which is integral with a support element and which comprises a coupling of the electromagnetic type with front linkage and adjustable induction current.